1. Field of the Invention
This invention relates to soil aerification (or “aeration”). More particularly, it relates to a method and apparatus for the aerification of turf grasses using a self-rotating turf drill.
2. Description of the Related Art
What is Aerification
Aerification is a mechanical process that creates more air space in the soil and promotes deeper rooting, thus helping plants stay healthy. In most cases, this is achieved by removing cores (often called plugs) and then filling the holes with topdressing. Topdressing is often a certain grade of sand which may have other amendments added to allow the soil to maintain air space, improve water penetration, and encourage healthy root growth. The sand is brushed or poured into the holes which are usually healed within several days.
The condition of turf largely depends on the events occurring below the surface. For grass to grow, deep healthy roots are needed, and roots require oxygen. In good soil, they receive oxygen from tiny pockets of air trapped between soil and sand particles. On a sports field, the everyday traffic from players combined with the weight of heavy mowing equipment causes the soil to become compacted and the air pockets on which the roots depend for oxygen are lost. Aerification is a mechanical process that creates more air space in the soil and promotes deeper rooting, water percolation and compaction relief.
The practice of aerating turf is becoming increasingly widespread. The benefits of aerification include:                improved water infiltration and better drainage                    Deeper penetration of fertilizers            Improved plant rooting            Thatch control            Increased stress tolerance                        Break up of sod layers that can restrict rooting and water movement        Release of toxic gases from soils        Increased drying and drainage of persistently wet soils        Loosening of soil, allowing for increased air space        Softening of sports fields to reduce risk of injury        
The principal reason for aerification is soil compaction relief. In addition, putting green aerification can provide for additional surface smoothing.
Compaction Relief
Definition of Compaction
Compaction of sports playing fields and golf course tees, greens and fairways is an inevitable product of their use—golf carts, maintenance machinery and feet all contribute to the process that is defined as “the consolidation of soil particles.” Compaction decreases water and oxygen movement in the soil, hinders root growth and lessens the ability of the soil to drain. Soil compaction causes these negative effects by turning macropores (larger voids in the soil largely responsible for drainage and air flow) into many micropores (smaller voids that hold water). As compaction increases, bulk density also usually increases, which means that more soil solids occupy a unit volume of soil, reducing the porosity.
With turfgrass, techniques used to relieve compaction must be effective without being highly visible. Aerification—either with solid tines that create a hole in the soil, or with hollow tines or drills that remove a core of soil—is one of the more common ways of improving compacted soils.
When a soil compaction condition is accompanied by excessive thatch buildup, as is almost always the case in poorly maintained turf, each condition contributes to the effect of the other. Thatch is a mat of undecomposed plant material (e.g., grass clippings) accumulated next to the soil in a grassy area (as a lawn, sports field or putting green). It is a tightly intermingled layer of living and dead stems, leaves and roots of grasses, which develops between the layer of green vegetation and the soil surface. When thatch exceeds about ½ inch of undecomposed material, it acts as a barrier to water and air infiltration into the soil below and will provide an environment encouraging turf diseases and harmful insects. Compacted soils, on the other hand, are subject to greater temperature extremes than loose soils, because of limited air movement; microbial activity necessary to thatch decomposition is reduced or halted.
Water that cannot penetrate the soil runs off or accumulates in low spots where it harbors fungus growth.
Alleviating either condition will help, but only when thatch is kept under control and the soil is properly aerified will turf have the best chance for healthy, vigorous growth and disease resistance.
The accumulation of organic matter (thatch) and fine particles (silt and/or clay) can, over time, produce a surface layer that reduces porosity. Aerification can modify the profile, improving oxygen, water, and root movement, especially when the use of hollow tines or turf drills is combined with core removal and backfilling channels with high-quality topdressing sand.
Prior Art Methods of Aerification
Turfgrass cultivation activities include hollow tine aerification, solid tine aerification, spiking, slicing, and water injection. These activities, to varying degrees, can reduce thatch, prepare turf for overseeding, and relieve soil compaction. Perhaps the best machine for working large areas is a piston driven aerator that thrusts the core cutters vertically. Direct up and down coring leaves a clearly defined hole. Drum-type roller aerators will work but may cause tearing damage to the remaining grass since this type of cutter enters the turf at one angle, moves in an arc with the drum movement, and is withdrawn at a different angle.
Solid Tine
Solid-tine aerification allows turf managers to aerate more frequently, since the procedure produces less surface disruption. Solid tines larger than ¼ inch in diameter open turf to allow water and air infiltration, but the process compresses displaced soil downward and to the sides. This actually increases soil compaction around newly created aerification holes. Repeated solid-tine aerification with larger-diameter tines can create a hardpan at the aerating depth.
Related to solid tine aerification are slicing and spiking aerifiers. Slicing, spiking, and solid tine aerification do not pull plugs of soil from the turf. Slicing aerifiers cut thin slits into the soil and spiking aerifiers cut thin, triangular-shaped holes in turf. While they do not relieve soil compaction as efficiently as hollow tine aerification, these practices cause less surface disruption and can be done anytime.
Hollow Tine
These devices pull out plugs of soil that are deposited on the surface. One of the most common operations that one can perform using a hollow tine aerator is conducting a soil exchange program, offering the professional an ideal opportunity to remove soil cores and replace them with a suitable top dressing, altering the soil profile.
Self-powered hollow tine aerifiers (core aerifiers) insert hollow tines into the soil, removing a soil plug ¼″ to ¾″ in diameter and 2″ to 12″ deep, depending or, soil type, soil moisture, and type of machine. Core spacing varies depending upon the make and model of the machine. In general, the more cores removed per square foot, the more effective the cultivation will be; removing fifteen to thirty cores per square foot is recommended. Hollow tine aerification is considered the most efficient compaction reliever of the prior art methods. It is preferably done during active turf growth.
Slitting
Using triangular blades ranging in size 100–250 mm (4″ to 10″), these machines create lots of short, narrow, close slits; slitting is useful for getting air down into the soil; it's quick; it does a fair job in dethatching; however, this approach is not highly effective at reducing compaction. Slitting also has its benefits, particularly in autumn when it can be employed to help ‘connect’ the surface of the soil with the underlying drainage layers. In the spring and summer, slitting ensures that water from rain and irrigation soak through the turf rather than being shed in a sideways fashion by the thatch.
Water Injection
Water injection aerification is a recently-introduced method of turf aerification. Water, under high pressure, is injected into the turf surface to relieve soil compaction. In addition, it can be used to inject turf management chemicals into the soil. It causes little surface disruption and can be done anytime during the growing season. This new technology has not been commonly available for use outside of golf course applications.
Deep Drill Aerification
Drill-type aerifiers employ rotating turf drills. The drill bits eliminate compaction along the sides and bottom of the aerification hole, and allow for quick and effective penetration even in heavily compacted soils including hardpan, muck and roots. The “gentle footprint” of drill-type aerifiers, in conjunction with the absence of cyclic vibration and the “straight in, straight out” action of the drill bits, gives this type of machine the capability of aerating fields that are wet, dry or experiencing periods of high stress.
Deep drill aerifiers are also preferred for use in all problem areas because the rotating drill bits will penetrate subsoil areas, where other machines tend to walk or bounce, often causing trauma to the playing surface. Turf drill bits fracture the cylinder wall without glazing, thereby allowing lateral movement of air and water. “Drill & Fill” aerifiers are available which back-fill the drilled holes with a selected top dressing, usually sand, thereby modifying the soil profile.
Turf drill bits are commercially available in ⅝″×12″, ⅝″×16″, ¾″×12″, and 1″×12″ sizes. One particular deep drill aerifier currently on the market produces 5″ spacing of holes. Drill aerification is especially preferred when one must penetrate hard soils. However, drill aerification is a very slow process as compared to reciprocating type aerifiers.
As noted above, aerification has the added benefit of smoothing the surface of a putting green. The process of punching holes and either reincorporating the plugs brought up or removing the plugs and filling the channels can offer some surface smoothing. Surface topdressing alone will fill/smooth low spots. The combination of aerifying and the follow-up topdressing will, over time, both fill low spots and soften high spots, resulting in more efficient surface smoothing than topdressing alone.